1. Field of the Invention
The present invention relates in general to a door window regulator for an automotive vehicle, and, more particularly, to a wire-type door window regulator having a wire tensioner.
2. Description of the Prior Art
In order to clarify the operation of the present invention, one conventional door window regulator will be outlined with reference to FIG. 5, which is disclosed in Japanese Patent First Provisional Publication No. 55-30095.
The door window regulator comprises a guide rail (a) secured to a door panel (not shown), a carrier member (b) slidably movable along the guide rail (a) and carrying thereon a window glass pane (c), pull-up and pull-down wires (d, e), each having a leading end fixed to the carrier member (b) and a drive unit (f) mounted to the door panel to drive the wires (d, e) upward or downward. Upon operation of the drive unit (f), the carrier member (b) is thus moved upward or downward together with the glass pane (c) along a path designated by reference (g). In order to compensate for an unavoidable permanent elongation of the wires (d, e), wire tensioners are arranged on the carrier member (b). Each tensioner comprises a wire end gripper (h, h') fixed to the leading end of each wire (d, e), a bracket (i, i') secured to the carrier member (b) and a coil spring (j, j') compressed between the wire end gripper and the corresponding bracket. By means of the coil springs (j, j'), the wires (d, e) are kept tensioned.
However, the window regulator as described hereinabove has the following drawbacks.
(1) Since the wire tensioners are arranged at laterally different positions of the carrier member, (b) the associated wires (d, e) extend along different ways, and the action points of the wires (d, e) to the carrier member (b) are compelled to change considerably depending on the direction in which the carrier member (b) moves, that is, depending on whether the carrier member (b) moves upward or downward. The change of the action points causes each wire (d, e) to run along different paths on its upward and downward movements, so that, when, for instance, the carrier member (b) is under its upward movement, the length of the pull-up wire (d) retracted by the drive unit (f) becomes different from that of the pull-down wire (e) released from the drive unit (f). This uneven travelling of the wires (d, e) tends to induce slippage of one wire on the winding drum of the drive unit (f) thereby impairing the operation of the window regulator.
(2) Because of the two bulky coil springs (j, j'), the carrier member (b) is bulky. As is known, the bulky construction is not desirable because of a limited space available in the door construction in which the window regulator is installed.
(3) Because of the coil springs (j, j'), which are forced to change their axial lengthes during operation of the window regulator, the determination of the length of each wire (d, e) must be made by taking the changeable length of each coil spring (j, j') into consideration, and this is very difficult.
(4) During operation of the drive unit (f) to effect upward or downward movement of the carrier member (b), a considerable degree of compression force is suddenly applied to the spring (j) or (j') because of the considerable weight of the glass pane (c) applied to the carrier member (b). This sometimes brings about undesirable jamming of the turns of the coil spring (j) or (j').